The present invention generally relates to inkjet and other types of printers and, more particularly, to the printhead portion of an inkjet printer.
Inkjet print cartridges operate by causing a small volume of ink to vaporize and be ejected from a firing chamber through one of a plurality of orifices so as to print a dot of ink on a recording medium such as paper. Typically, the orifices are arranged in one or more linear nozzle arrays. The properly sequenced ejection of ink from each orifice causes characters or other images to be printed in a swath across the paper.
An inkjet printhead generally includes ink channels to supply ink from an ink reservoir to each vaporization chamber (i.e., firing chamber) proximate to an orifice; a nozzle member in which the orifices are formed; and a silicon substrate containing a series of thin film resistors, one resistor per vaporization chamber.
To print a single dot of ink in a thermal inkjet printer, an electrical current from an external power supply is passed through a selected thin film resistor. The resistor is then heated, in turn superheating a thin layer of the adjacent ink within a vaporization chamber, causing explosive vaporization, and, consequently, causing a droplet of ink to be ejected through an associated orifice onto the paper.
In an inkjet printhead, described in U.S. Pat. No. 4,683,481 to Johnson, entitled "Thermal Ink Jet Common-Slotted Ink Feed Printhead," ink is fed from an ink reservoir to the various vaporization chambers through an elongated hole formed in the substrate. The ink then flows to a manifold area, formed in a barrier layer between the substrate and a nozzle member, then into a plurality of ink channels, and finally into the various vaporization chambers. This design may be classified as a "center" feed design, with side electrical interconnects to a flex-circuit along the full length of the substrate. Ink is fed to the vaporization chambers from a central location then distributed outward into the vaporization chambers which contain the firing resistors. Some disadvantages of this type of ink feed design are that manufacturing time is required to make the hole in the substrate, and the required substrate area is increased by at least the area of the hole and also by extra substrate at both ends of the hole to provide structural integrity. Also, once the hole is formed, the substrate is relatively fragile, making handling more difficult. Such prior printhead design limited the ability of printheads to have compact stable substrates with wide swath high nozzle densities and the lower operating temperatures required for increased resolution and throughput. Print resolution depends on the density of ink-ejecting orifices and heating resistors formed on the cartridge printhead substrate. Modern circuit fabrication techniques allow the placement of substantial numbers of resistors on a single printhead substrate. However, the number of resistors applied to the substrate is limited by the number and location of the conductive components used to electrically connect the printhead to external driver circuitry in the printer unit. Specifically, an increasingly large number of firing resistors requires a correspondingly large number of interconnection pads, leads, grounds and the like. This increase in components and interconnects and the resulting increase in substrate size causes greater manufacturing/production costs, increases the probability that defects will occur during the manufacturing process, and increases the heat generated during high frequency operation.